pop3 test server: send terminating ".CRLF" only

With commit 035ef06bda applied, the test pop3 server needs to send
".\r\n" as the body terminating sequence and there needs to be a final
CRLF in the actual body in the test data file.

tests/data/test800

@@ -10,13 +10,13 @@ RETR
 # Server-side
 <reply>
 <data>
-From: me@somewhere
-To: fake@nowhere
-
-body
-
---
-  yours sincerely
+From: me@somewhere
+To: fake@nowhere
+
+body
+
+--
+  yours sincerely
 </data>
 </reply>